Urate oxidase is a peroxisomal enzyme with four equal subunits that convert uric acid to allantoin, a more soluble metabolite for excretion. The usage of uricase as a drug in medicine is to treat hyperuricemia. Many microorganisms have been used for uricase production such as Streptomyces exfoliates, Pseudomonas aeruginosa, and Aspergillus flavus. In this study, soil samples were collected and then cultured in a screening medium including uric acid as the sole carbon source. Samples with the higher ability of uricase production were selected for enzyme assay. Enzyme activity was measured by spectrophotometry and the sample with the maximal uricase activity was identified as Aspergillus niger and selected for further studies. According to the results of experiments, the optimized temperature for enzyme production by Aspergillus niger was determined to be 35±2°C. The best carbon and nitrogen source was glucose and NH4NO3, and the highest enzyme activity was observed in the presence of Cu2+ ion.